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Abstract: Regeneration of baldcypress (Taxodium distichum (L.) Rich.) and water tupelo (Nyssa aquatica L.) in swamps of the deltaic plain of the Mississippi River are of major importance for ecosystem sustainability and forest management in the context of regional hydrological changes. Water tupelo often forms prolific sprouts from cut stumps, and baldcypress is one of few conifers to produce stump sprouts capable of becoming full-grown trees. Previous studies have addressed early survival of baldcypress stump sprouts, but have not addressed the likelihood of sprouts becoming an important component of mature stands. We surveyed stands in southeastern Louisiana that were partially logged 10–41 years ago to determine if stump sprouts are an important mechanism of regeneration. At each site we inventoried stumps and measured stump height and diameter, presence and number of sprouts, sprout height, and water depth. We determined age and diameter growth rate for the largest sprout from each stump from increment cores. The majority of stumps did not have surviving sprouts. Baldcypress sprout survival was about the same (median 10%) as previously found for stumps up to 7 years old, so it appears that, although mortality is high soon after sprouting, it is low after age 10. Water tupelo sprouting was rare at our sites but it was not clear whether this may have been because trees were not cut at our sample locations. Baldcypress stump sprouts were more likely to survive on shorter, smaller-diameter stumps, and baldcypress sprout growth was greatest on drier sites with less competition from overstory trees. Surviving baldcypress stump sprouts had high growth rates, but were not regularly spatially distributed within stands and many had advancing decay from stumps into sprouts. [Copyright &y& Elsevier]

1. The wetlands of the Atchafalaya Delta. Louisiana are characterized by a warm climate, highly fertile sediments, and an absence of moisture limitations. Consequently. vegetation succession (on islands that emerged in 1973) was expected to occur relatively rapidly. 2. From 1980 until 1986 annual surveys of vegetation cover and substrate elevation were conducted on 110 permanent plots along six transect lines crossing (our islands. In addition, to evaluate the effect of herbivory (predominantly by Myocastor coypus, nutria or coypu), four 50-m × 40-m exclosures and four control plots were constructed on two of the islands. 3. Community structure changed dramatically through time along the permanent transects. Because several species shifted in elevational range. ordination (using detrended correspondence analysis) only generally separated plant communities into different elevational zones. 4. The 20 most dominant species, representing 95% of the total cover, were classified into three distinct groups according to cover pattern: (i) species that increased in abundance through time and stabilized within particular elevational zones (e.g. Colocasia esculenta, Justicia ovata, Leersia oryzoides, Polygonum punctatum, Scirpus americans. Vigna luteola). (ii) species with relatively stable cover over time (e.g. .Aeschynomene indica, Eleocharis spp.. Panicum sp.. Sagittaria lancifolia. Salix nigra, Scirpus validus, Tvpha domingensis), and (iii) species that occurred over a wide range initially, but eventually disappeared at low elevations (e.g. Ammannia cuccinea, Cyperus difformis. Hydrocotyle sp.. Mikania scandens. Sagittaria latifolia. Sagittaria platyphylla, Sphenoclea zeylandica). 5. Two general trends across all islands through time involved a decrease in vegetated area and a marked increase in species diversity. The decrease in vegetated area is attributable to increased grazing damage by nutria combined with the negative effect of prolonged flooding. [ABSTRACT FROM AUTHOR]

We attempted to determine the extent to which benthic diatoms contribute to water column primary productivity in shallow-water estuaries and to elucidate the primary mechanisms responsible for suspending the diatoms. A preliminary study conducted in Mugu Lagoon, California indicated that productivity of ocean water entering the lagoon during flood tides was often several orders of magnitude less than that of the same water mass about 3 h later. Benthic pennate diatoms displaced from the sediments into the water column accounted for the increase. A more detailed study was conducted in Barataria Estuary. Louisiana where, for one month, daily measurements were made of benthic and water column productivity and several other environmental variables. During the month, the relationship between water column and benthic primary productivity varied from strongly negative to weakly negative to positive. K-systems analysis indicated that factors comprised of wave height, meteorological tides, astronomical tides, and benthic productivity and standing crop accounted for the full range of variation in water column productivity, Benthic pennate diatoms represented an average of 74% of the diatom taxa in water column samples. We conclude that the primary productivity of well-mixed shallow estuarine waters is often greatly augmented by displaced benthic algae. [ABSTRACT FROM AUTHOR]